The machining efficiency of an electrode wire EDM apparatus is greatly improved by applying across the machining zone between the electrode wire and the electrode workpiece current pulses of very short duration which are provided with a sharp, steep leading edge. Steep leading edge pulses can be obtained only if the pulse generator circuit connected across the electrodes has a very low impedance and inductance. It is therefore advantageous to decrease as much as possible the self-inductance of the electrical connections between the pulse generator, the electrode wire and the workpiece.
A known method for achieving such a result consists in connecting the pulse generator to the electrode wire by means of a first sliding contact mounted on one of the guiding arms of the electrode wire and to the workpiece by means of a second sliding contact supported by the same electrode wire guiding arm, the second sliding contact being maintained in engagement with the surface of the workpiece proximate the guiding arm. Such a device, however, presents the inconvenience of being practical only if the workpiece surface, with which the sliding contact is engaged, has been prepared such as to be relatively flat and to provide a good electrical contact. If the workpiece has a variable thickness, or if its surface is rough or is a poor conductor of electricity, such an arrangement is not practical.
The present invention remedies the inconveniences and limitations of the prior art devices. The invention permits the self-inductance of the circuit supplying the electrical discharge pulses to the electrodes to be reduced to a minimum, and does not rely on the shape of the workpiece or on the electrical conductance of the workpiece surface for its operation.